FIG. 19 illustrates an example of conventional construction of a steering apparatus of an automobile. The steering apparatus is constructed such that the rotation of the steering wheel 1 is transmitted to the input shaft 3 of a steering gear unit 2, and as the input shaft 3 rotates, the rotation pushes or pulls a pair of right and left tie rods 4, which applies a steering angle to the front wheels. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and the steering shaft 5, being inserted in the axial direction through a cylindrical shaped steering column 6, is supported by the steering column 6 so as to rotate freely. Moreover, the front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 by way of a universal joint 7, and the front end section of the intermediate shaft 8 is connected to the input shaft 3 by way of a different universal joint 9. In the example in the figure, a tilt mechanism for adjusting the up-down position of the steering wheel 1, a telescopic mechanism for adjusting the forward-backward position, and an electric power-steering apparatus that uses an electric motor 10 as an auxiliary power source that makes it possible to reduce the force required for operating the steering wheel 1 are assembled.
There is a need for construction in a steering apparatus for an automobile that makes it possible to protect the driver during a collision accident. For example, the intermediate shaft 8 is constructed so as to be able to transmit torque, as well as to be able to contract over the entire length due to an impact load; and during a primary collision in a collision accident in which the automobile collides with another automobile, contraction of the intermediate shaft 8 prevents the steering wheel 1 from displacing toward the rear and being pushed up toward the body of the driver regardless of whether the steering gear unit 2 displaces toward the rear. Moreover, during a collision accident, after the primary collision, a secondary collision occurs in which the body of the driver collides with the steering wheel 1. In order to ease the impact that is applied to the body of the driver during this secondary collision, the steering column 6 is supported by the vehicle so as to be able to break away when a large force is applied in the forward direction.
FIG. 20 to FIG. 24 illustrate a first example of conventional construction of an impact absorbing steering apparatus as disclosed in JP 2011-148354 (A) that comprises this kind of impact absorbing mechanism. In this construction, a column-side bracket 11 that supports the middle section of the steering column 6 is supported by a vehicle-side bracket 15 that is fastened to the vehicle by way of a pair of right and left locking capsules 20 and bolts 21 (see FIG. 19) so as to be able to break away when a large force is applied in the forward direction. Moreover, as the secondary collision advances, in order to absorb the impact energy that is applied to the steering column 6 from the body of the driver as the steering column 6 displaces in the forward direction, a pair of right and left energy absorbing members 22 are provided between a portion that displaces in the forward direction together with the steering column 6 and a portion that is supported by the vehicle or by the vehicle-side bracket 15 that does not displace in the forward direction.
The column-side bracket 11 is obtained by bending a metal plate such as steel plate, and has a pair of right and left support plate sections 13 that are provided in the up-down direction, and a pair of right and left installation plate sections 14 that are provided so as to protrude in the left-right direction of the steering column 6 from the top end sections of these support plate sections 13. The installation plate sections 14 can also be constructed from a single plate. Moreover, part of the edges on the bottom ends of the support plate sections 13 are connected by a connecting section such that the column-side bracket 11 is a single body. Of these installation plate sections 14, locking notches 23 are provided in positions on both the right and left sides of the steering column 6, and are open on the rear end edges of the installation plate sections 14. These locking notches 23 have a trapezoidal shape such that the width dimension becomes smaller going toward the front (back side). There are also locking capsules 20 that are assembled inside these locking notches 23. The locking capsules 20 are obtained by injection molding of synthetic resin, or by die casting of a light alloy, and have locking grooves 24 on the right and left side surfaces of each. The space between the bottom surfaces of a pair of locking grooves 24 that are formed in these side surfaces becomes more narrow going toward the front to correspond with the width of the locking notches 23.
This kind of locking capsule 20 is supported by the installation plate section 14 by engaging the locking grooves 24 with the portions on both sides of the locking notch 23 in part of the installation plate section 14. Moreover, with the small through holes 25 that are formed in the portions on both sides of the locking notch 23 in part of the installation plate section 14 aligned with the small through holes 26 that are formed in the locking capsule 20, locking pins (not illustrated in the figure) that are made of synthetic resin or light alloy are located so as to span between these small through holes 25, 26. With these locking pins, the locking capsule 20 is supported by the installation plate section 14 so as to break away toward the rear only when a large impact load is applied. There are locking capsules having different numbers of through holes 25, 26 and locations where they are formed. Moreover, instead of small through holes 25 in the installation plate section 14 side, it is also possible to provide small notches that open to the locking notch 23.
The locking capsule 20 is supported by and fasted to the vehicle-side bracket by the bolt 21 that is inserted from the bottom through the through hole 43 provided in the center section of the locking capsule 20. Therefore, a screw hole is directly formed in the vehicle-side bracket 15 for screwing the bolt 21 into, or a nut is fastened to the top surface of the vehicle-side bracket 15. The locking capsule 20 and installation plate section 14 are connected with somewhat large strength and rigidity by the engagement between the portions on both sides of the locking notch 23 and the locking grooves 24, and locking pins that span between the small through holes 25, 26. Therefore, normally, the column-side bracket 11 is firmly supported by the vehicle.
On the other hand, an energy absorbing members 22 are provided between the locking capsules 20 that are supported by the vehicle-side bracket 15 and the column-side bracket 11 that displaces in the forward direction together with the steering column 6. An energy absorbing member 22 is obtained by bending a wire material that can plastically deform such as mild steel or stainless steel. More specifically, with the center section as a straight base section 27, both end sections of this base section 27 are bent at right angles toward the front to form a pair of impact absorbing sections 28. By bending back the middle sections of these impact absorbing sections 28 downward and toward rear in a U shape, bent back curved sections 29 are formed. The base section 27 of each of the energy absorbing members 22 locks into a support groove 30 that is provided in the top surface of the rear section of the locking capsule 20, and the inner circumferential edges of the bent back curved sections 29 engage with the edge on the front end of the installation plate section 14.
In the case illustrated in the figure, in order to simplify the work of assembling the locking capsules 20 in the vehicle-side bracket 15, a hanger bracket 31 is mounted on the locking capsule 20 so as to cover the top and bottom surfaces and part of the rear end surface of the locking capsule 20. So as to provide the hanger bracket 31, the base section 27 of the energy absorbing member 22 is locked in the support groove 30 of the locking capsule 20. When this hanger bracket 31 is not provided, it is possible to omit the support groove 30 and to lock the base section 27 to the side surface on the rear side of the locking capsule 20. The construction of a hanger bracket 31 is disclosed in JP 2011-148354 (A), JP 2010-13010 (A) and JP 2011-131682 (A), and it is not related to the scope of this invention, so a detailed explanation thereof is omitted.
When an automobile, in which this kind of impact absorbing steering apparatus is installed, is involved in a collision accident, first, the front section of the vehicles is smashed in by the primary collision, and the steering column 6 is pushed toward the rear, in this state, the engagement between the locking capsule 20 and the locking notch 23 is maintained, and displacement of the steering column 6 toward the rear is prevented. However, during a secondary collision, when a strong force is applied in the forward direction to the steering column 6 from the steering wheel 1, the locking pins that span between the through holes 25, 26 shear off, and with the locking capsules 20 remaining in that position, the installation plate sections 14 displace toward the front, which allows the steering wheel 1 to displace in the forward direction.
When the installation plate sections 14 displace in the forward direction due to a secondary collision, the bent back curved sections 29 of the energy absorbing members 22 move toward the tip end sections of the impact absorbing sections 28 while being stroked by the edges on the front ends of the installation plate sections 14, and allows the support bracket 11, which includes the installation plate sections 14 to displace in the forward direction. When this happens, the impact energy that is applied to the support bracket 11 during a secondary collision is absorbed by the plastic deformation of the impact absorbing sections 28, which eases the impact that is applied to the body of the driver. In order to effectively perform this kind of energy absorption, stroking sections 32, the front surfaces thereof being convex curved surfaces (stroking surfaces), are formed in the portions that face the inner circumferential edges of the bent back curved sections 29 on the front end edges of each of the installation plate sections 14. Moreover, a pair of small through holes (not illustrated in the figure) are formed in part of the downward hanging plate sections 33 that are bent downward from the tip end edges of the stroking sections 32, and the portions of the impact absorbing sections 28 that are nearer the tip ends than the bent back curved sections 29 are inserted though these small through holes. With this kind of construction, the tip end sides of the impact absorbing sections 28 is prevented from displacing downward during a secondary collision, which keeps the bent back curved sections 29 from opening up, and thus it is possible for the bent back curved sections 29 to move toward the tip ends of the impact absorbing sections 28 while being stroked.
FIG. 25 to FIG. 28 illustrate a second example of conventional construction of an impact absorbing steering apparatus as disclosed in JP 3,409,572 (B2). In this second example of conventional construction, there is neither a tilt mechanism nor a telescopic mechanism, and a rear-side support bracket 35, which is one of the front/rear column-side brackets composed of a single plate obtained by bending a steel plate having sufficient rigidity is fastened to the middle section of the steering column 6a by welding. Installation plate sections 14a that are provided on the right and left, and a front-side downward hanging plate section 36 that is bent downward from the front end edge of the stroking sections 32a that are provided on the front end edges of the installation plate sections 14a, and a rear-side downward hanging plate section 37 that is bent downward from the center section on the rear end edges of the installation plate sections 14a is formed on the rear-side support bracket 35. A circular hole 38 is formed on the bottom side of the center section of the front-side downward hanging plate section 36, and a semicircular notch 39 is formed on the bottom edge of the rear-side downward hanging plate section 37. The curvature of the circular hole 38 and the notch 39 nearly coincide with the curvature of the outer circumferential surface of the steering column 6a. The rear-side support bracket 35 is fastened to the outer circumferential surface of the middle section of the steering column 6a, with the steering column 6a inserted through the circular hole 38 and the outer circumferential surface of the steering column 6a abutted on the notch 39, by welding the inner circumferential edges of the circular hole 38 and notch 39 to the outer circumferential surface of the steering column 6a. 
In this second example of conventional construction as well, locking notches 23 that are open on the rear end edge side of the installation plate section 14a are formed in each of the installation plate sections 14a, and locking capsules 20a are supported on the inside of each of the locking notches 23. With locking pins (not illustrated in the figure) spanning between small notches (not illustrated in the figure) that are provided in the perimeter edges of the locking notches 23 and that are open to the locking notches 23, and small through holes 26 that are formed in the locking capsules 20a, the locking capsules 20a are supported by and fastened to the vehicle-side bracket 15 that is fastened to the vehicle by bolts 21 or studs that are inserted through the through holes 43 that are formed in the center sections of the locking capsules 20a. With this kind of construction, as in the first example of conventional construction, the rear-side support bracket 35 that supports the middle section of the steering column 6a is supported by the vehicle-side bracket 15, which is fastened to the vehicle, by way of the locking pins, the pair of right and left locking capsules 20a and bolts 21 so as to be able to break away when a large force is applied in the forward direction.
In this second example of conventional construction as well, energy absorbing members 22a are provided between the locking capsules 20a that are supported by the vehicle-side bracket 15 and the rear-side support bracket 35 that displace in the forward direction together with the steering column 6a. The energy absorbing members 22a are obtained by bending metal wire that can plastically deform, with each energy absorbing member 22a comprising a base section 27a that is formed in the center section of the metal wire, a pair of impact absorbing sections 28a that are formed by bending both end sections of the base section 27a at right angles toward the front, and bent back curved sections 29a that are formed in the middle sections of these impact absorbing sections 28a bending back these middle section downward and toward the rear into U shapes. In this second example of conventional construction, instead of providing a hanger bracket, the base end sections 27a of the pair of energy absorbing members 22a are locked on the side surface of the rear side of the pair of right and left locking capsules 20a, and the inner edge of the bent back curved sections 29a engage with the front end edges of the installation plate sections 14a. Moreover, of the impact absorbing sections 28a, by bending the connecting sections between the base sections 27a and the bent back curved sections 29a directions toward each other, the distance between the bent back curved sections 29a and between the sides of the impact absorbing sections 28a that are further toward the tip end side than the bent back curved sections 29a is reduced, and when the base sections 27a are locked to the locking capsules 20a, the work of attaching the rear-side support bracket 35 to the support plate 15 can be easily performed so that these engaged members do not accidentally separate.
In this second example of conventional construction, a space 41 having a dimension “t” is set between the bent back curved section 29a of the energy absorbing members 22a and the convex curved surface of the stroking section 32a (see FIG. 25). Therefore, during a secondary collision, the installation plate sections 14a is displaced forward by a dimension “t”, after which, the energy absorbing members 22a absorb the impact load of a secondary collision by allowing the bent back curved sections 29a to move toward the tip end sections of the impact absorbing sections 28a while being stroked by the stroking sections 32a. The other construction and functions of this second example of conventional construction are the same as in the first example of conventional construction.
In the impact absorbing steering apparatus of both the first and second examples of conventional construction, there is room for improvement from the aspect of more completely protecting the driver during a secondary collision. In other words, in the case of the first example of conventional construction, the inner circumferential edge sections of the pair of bent back curved sections 29 of each of energy absorbing members 22 come in contact with the stroking sections 32 with nearly the same positional relationship. On the other hand, in the case of the second example of conventional construction, the inner edge sections of the pair of bent back curved sections 29a of each of energy absorbing members 22a face the respective stroking sections 32a through spaces 41 having the same distance and the same positional relationship. In this way, in the case of the impact absorbing steering apparatuses of the first and second examples of conventional construction, all of the four bent back curved sections 29, 29a start to be stroked at the same time. However, in order to completely protect the driver, preferably, immediately after the secondary collision begins, the load required for causing the steering wheel 1 (see FIG. 19) to displace in the forward direction is kept low, and this load increases as the secondary collision advances. In other words, preferably, the amount of the impact load that is absorbed by the energy absorbing members 22, 22a is initially small at the beginning of displacement, and gradually increases.
JP 2007-223486 (A) discloses construction in which in an energy absorbing member that is obtained by bending wire that is plastically deformable, the positions in the forward-backward direction of the pair of bent back curved sections are different, and the load required for causing the steering wheel to displace in the forward direction immediately after a secondary collision begins is reduced. However, this energy absorbing member has an increased width dimension, so in addition to special construction for causing the bent back curved section to plastically deform during a secondary collision, the size of the energy absorbing member is increased in order to maintain the total amount of impact energy that can be absorbed, and thus the manufacturing cost increases, so is not practical construction.
Moreover, in order to change the characteristics of the energy absorbing members for absorbing the impact load, a structure where a through hole is provided in the metal plate is disclosed in JP 2001-114113 (A), and a structure where the metal wire is heat-treated or treated with high-frequency hardening or a structure where the cross-sectional area of the metal wire is varied is disclosed in JP 2008-230266 (A) and JP2007-302012 (A). However, in the case of the invention disclosed in JP 2001-114113 (A), a metal plate is used so the cost increases when compared with the case of using a metal wire. Moreover, in the case of the invention disclosed in JP 2008-230266 (A) and JP 2007-302012 (A), setting the heat treatment conditions or hardening conditions is difficult, so the cost increases, which alone makes it difficult to obtain stable performance. Furthermore, in the case of construction of simply changing the cross-sectional area, the cost of the wire increases.